How many standby redo log files you have configured?
Ensure you have same size of standby redo log files as Online redo log files (and) create same or more number of standby redo log files than Online redo log files.
and you must see in Standby alert log file as below

Media Recovery Waiting for thread 1 sequence 2717 (in transit)

If it is in transit , then means writing redo into standby redo log files. So most probably you may have issues with standby redo log files.